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SubjectNFS root and Floppy Fallback ...

Hi Marcelo!

Here is my fix for the NFS root issue and optional
floppy fallback ...

the (short) story: root_dev_setup() calls name_to_kdev_t()
which searches root_dev_names[], and if no device can be
found, (0:0) is returned, which in turn, if NFS root is
enabled, leads to a doomed NFS root attempt, finally
leading to some ancient floppy fallback ...

the first patch 'corrects' the behaviour, in such way,
that only root=/dev/nfs or a root device of (0:255) will
lead to the NFS root attempt (I guess this was the
original intention of the author).

the second patch adds a config option to disable the
Floppy Fallback entirely, which is disabled by default
(so no changes to the default behaviour).

best,
Herbert


-----
diff -NurbP --minimal linux-2.4.22-pre3/include/linux/nfs.h linux-2.4.22-pre3-fix/include/linux/nfs.h
--- linux-2.4.22-pre3/include/linux/nfs.h Sat Apr 1 18:04:27 2000
+++ linux-2.4.22-pre3-fix/include/linux/nfs.h Wed Jul 9 22:39:37 2003
@@ -30,6 +30,9 @@
#define NFS_MNT_PROGRAM 100005
#define NFS_MNT_PORT 627

+#define NFS_MAJOR UNNAMED_MAJOR
+#define NFS_MINOR 0xff
+
/*
* NFS stats. The good thing with these values is that NFSv3 errors are
* a superset of NFSv2 errors (with the exception of NFSERR_WFLUSH which
diff -NurbP --minimal linux-2.4.22-pre3/init/do_mounts.c linux-2.4.22-pre3-fix/init/do_mounts.c
--- linux-2.4.22-pre3/init/do_mounts.c Sun Jul 6 22:55:07 2003
+++ linux-2.4.22-pre3-fix/init/do_mounts.c Wed Jul 9 22:41:43 2003
@@ -88,7 +88,7 @@
const char *name;
const int num;
} root_dev_names[] __initdata = {
- { "nfs", 0x00ff },
+ { "nfs", MKDEV(NFS_MAJOR, NFS_MINOR) },
{ "hda", 0x0300 },
{ "hdb", 0x0340 },
{ "loop", 0x0700 },
@@ -759,7 +759,8 @@
static void __init mount_root(void)
{
#ifdef CONFIG_ROOT_NFS
- if (MAJOR(ROOT_DEV) == UNNAMED_MAJOR) {
+ if (MAJOR(ROOT_DEV) == NFS_MAJOR
+ && MINOR(ROOT_DEV) == NFS_MINOR) {
if (mount_nfs_root()) {
sys_chdir("/root");
ROOT_DEV = current->fs->pwdmnt->mnt_sb->s_dev;

-----
diff -NurbP --minimal linux-2.4.22-pre3-fix/Documentation/Configure.help linux-2.4.22-pre3-fix-ffb/Documentation/Configure.help
--- linux-2.4.22-pre3-fix/Documentation/Configure.help Sun Jul 6 22:54:52 2003
+++ linux-2.4.22-pre3-fix-ffb/Documentation/Configure.help Wed Jul 9 23:00:08 2003
@@ -15942,6 +15942,18 @@

Most people say N here.

+Disable Fallback to Floppy
+CONFIG_NO_FLOPPY_FALLBACK
+ If root file system on NFS is enabled but the root device isn't
+ /dev/nfs (or the NFS root can not be mounted for any other reason)
+ the kernel usually falls back to a floppy boot.
+
+ This option will disable the default behaviour, which could be a
+ security risk, allowing either to boot from a specified root device
+ or not at all.
+
+ If unsure say N here.
+
NFS server support
CONFIG_NFSD
If you want your Linux box to act as an NFS *server*, so that other
diff -NurbP --minimal linux-2.4.22-pre3-fix/fs/Config.in linux-2.4.22-pre3-fix-ffb/fs/Config.in
--- linux-2.4.22-pre3-fix/fs/Config.in Sun Jul 6 22:55:05 2003
+++ linux-2.4.22-pre3-fix-ffb/fs/Config.in Wed Jul 9 22:49:40 2003
@@ -105,6 +105,7 @@
dep_tristate 'NFS file system support' CONFIG_NFS_FS $CONFIG_INET
dep_mbool ' Provide NFSv3 client support' CONFIG_NFS_V3 $CONFIG_NFS_FS
dep_bool ' Root file system on NFS' CONFIG_ROOT_NFS $CONFIG_NFS_FS $CONFIG_IP_PNP
+ dep_bool ' Disable Floppy Fallback' CONFIG_NO_FLOPPY_FALLBACK $CONFIG_ROOT_NFS

dep_tristate 'NFS server support' CONFIG_NFSD $CONFIG_INET
dep_mbool ' Provide NFSv3 server support' CONFIG_NFSD_V3 $CONFIG_NFSD
diff -NurbP --minimal linux-2.4.22-pre3-fix/init/do_mounts.c linux-2.4.22-pre3-fix-ffb/init/do_mounts.c
--- linux-2.4.22-pre3-fix/init/do_mounts.c Wed Jul 9 22:48:48 2003
+++ linux-2.4.22-pre3-fix-ffb/init/do_mounts.c Wed Jul 9 22:49:40 2003
@@ -767,8 +767,10 @@
printk("VFS: Mounted root (nfs filesystem).\n");
return;
}
+# ifndef CONFIG_NO_FLOPPY_FALLBACK
printk(KERN_ERR "VFS: Unable to mount root fs via NFS, trying floppy.\n");
ROOT_DEV = MKDEV(FLOPPY_MAJOR, 0);
+# endif
}
#endif
devfs_make_root(root_device_name);


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